# How often to set tire pressure

The recommended tire pressure in my van is 35psi. Two weeks ago I set the pressure when temps were around -20C. This week temps are hovering around zero, and the tires report around 38psi. Should I deflate them, even though temperatures will dip again in about a week?

What is a reasonable threshold to decide that a departure from the placard pressure deserves to inflate/deflate the tire?

Edit: I guess I was not clear enough. I have real time monitoring; that is, I can see the pressure of each of the four tires at any time. So, the question is not about checking. What I mean is, if I start the car in the morning and I see that the tires are at 36psi, should go and release 1psi right away?

• A few psi isn't a big deal, especially if they are all reading nearly the same. Relax man, just drive the car. I mean, seriously, what do you think is going to happen if you drive on tires that are 1psi over inflated? What are you worried about?
– cory
Commented Jan 17, 2017 at 16:31
• @cory: of course I don't touch the tires if they are 1psi off. But, what about 2psi? 3psi? 5psi? Where's the limit? That's precisely my question. Commented Jan 17, 2017 at 16:32

In some countries, you are meant to check lights tyres etc before you drive the vehicle for the first time that day... So, I find that I check my tyres at least once a week and if they look different more often. The ambient temperature and pressure cause the tyre pressure to drift / change from the expected setting.

• It looks like I didn't formulate the question clearly; please see the edit. Commented Jan 17, 2017 at 12:37
• Already added an interesting site you should look at below, but higher is ok within limits, low is to be avoided... Commented Jan 17, 2017 at 16:22

Of course there is a gap between what is optimum and what is reasonble to achieve. For example, you could check them once a year or stop every few miles during your trip to check them. Neither of these are reasonable!

I go by checking them each time the expected climate is changing or during periodic rotation of tyres.

For me, its reasonable this way because the climate in my area is quite mild and does not change drastically throughout each season. So I am able to adjust a few PSI as the seasons change. If I do it more often, I find I am checking and finding all the pressures are correct. I also check them before any long road trip. I do visual checks during cleaning.

In your case, I would prefer to adjust them for a 20C change in temperature, even if it means doing it weekly. Make it as easy as possible for yourself, have the air compressor and gloves ready in the vehicle so that its as convenient as possible to do routinely.

Otherwise, you may decide a compromise pressure will get you through 0C and 20C, this would a PSI number that gets you close enough during both expected temperatures. (I don't encourage this way, just adding for information.)

Update based on comment

This website claims: "under inflated by 15 psi (1 bar) lead to 6% greater fuel consumption."

Another website also has some figures for a particular Honda Accord:

• "6 psi below the recommended spec suffers a 5 percent decrease in fuel economy."
• "inflated 6 psi below spec, would wear out 25 percent faster."
• "tire pressure monitoring systems are designed to alert the driver only if a tire's pressure is 25 percent or more below specification, which is already well into the danger zone."

My advice is, no compromise on a safety item is acceptable.

• Checking is not the issue: the issue is precisely what compromise is acceptable. Commented Jan 17, 2017 at 12:37
• @MartinArgerami I don't think this is defined or documented anywhere by industry professionals or manufacturers because a compromise on safety is not endorsed but I will try to update my answer. Commented Jan 17, 2017 at 13:13
• So, if you want to read this it may help... : popularmechanics.com/cars/how-to/a3121/… Commented Jan 17, 2017 at 16:20